Investigating the Critical Mineral Systems of the Canadian Shield of Northeastern Alberta: A Summary of 2023 Field Work in Leland Lakes and Andrew Lake Areas

The Leland Lakes and Andrew Lake areas of the Canadian Shield in northeastern Alberta were investigated for their critical mineral potential, with a 2023 fieldwork program that included detailed geological mapping, geochemical sampling, and geophysical surveys. The local geology includes Archean and Paleoproterozoic quartzofeldspathic gneisses of the Taltson basement complex (TBC) with locally abundant bands and intrusions of mafic amphibolite that are overlain by high-grade, deformed, metasedimentary rocks of the Paleoproterozoic Rutledge River complex. These components were intruded by voluminous ca. 1.99–1.92 Ga, I- to S-type, granitoid magmas of the Taltson magmatic zone (TMZ). Paleoproterozoic to Mesoproterozoic metasedimentary rocks of the Athabasca Group, exposed at the southeastern edge of the shield in Alberta, unconformably overlie these older basement rocks. 

Field-based structural mapping and integrated geochemical analyses reveal a polyphase deformation history culminating in crustal thickening, arc magmatism, and transpressional shear zones. The earliest recognizable deformation phase (D1; ca. 2.13–1.96 Ga) involved isoclinal folding (F1) and development of a steeply dipping, composite fabric (S1-x-S1) under high-grade metamorphic conditions (M1), facilitating anatexis of rare-earth-element (REE)–enriched metasedimentary rocks and the generation of early granitoids and pegmatites. Upper-amphibolite- to granulite-facies conditions persisted or were renewed during the primary orogenic episode (D2; ca. 1.94–1.93 Ga), which produced doubly plunging F2 folds and a pervasive S1-2 gneissosity. Synchronous, voluminous magmatism emplaced granitoids that exhibit a transition from strongly arc-type signatures (e.g., Arch Lake, ca. 1.938 Ga) to more peraluminous, syncollisional compositions (e.g., Slave granitoid, ca. 1.934 Ga), reflecting increasing crustal thickness. Peak thermal conditions (M2) supported partial melting, syntectonic pegmatite emplacement, and localized mineralization. As shortening evolved into transpression, major deep-seated shear zones nucleated along F2 axial planes. Subsequent deformation (D3, D4), low-grade retrogression (M3), and related hydrothermal activity persisted well beyond the ca. 1.93 Ga magmatic peak. These findings support an orogenic model where subduction-driven crustal shortening shaped the western margin of the Rae craton. Overall, they emphasize a subduction-to-collision continuum in the southern TMZ, with repeated high-grade metamorphism and crustal reworking playing a key role in its critical mineral potential. 

Results of the lithogeochemical and petrographic analyses highlight significant potential of the TBC to host igneous REE mineralization. Pegmatites in the Andrew Lake study area exhibit strong light rare-earth-element (LREE) enrichment and are classified within the abyssal-LREE (U-Th-Ti) subclass of pegmatites. The pegmatites are similar to those at the Alces Lake area, approximately 120 km east in northwestern Saskatchewan, which host significant concentrations of REEs. Pegmatites in both study areas formed under mid- to high-grade metamorphic conditions within structurally favourable zones and are enriched in LREEs and depleted in heavy rare-earth elements. The Leland Lakes shear zone (LLSZ) is a promising target for gold and critical metals exploration, including Cu, Ni, Cr, and Co. The structural control of these occurrences, highlighted by the alignment with a magnetic break in aeromagnetic data and visible in bedrock exposures due to a recent forest fire, underscores the importance of the LLSZ as a promising target for future exploration. Assay results from sulphide-rich metasedimentary rocks, green fuchsitic veins, and mafic enclaves in this area demonstrate substantial concentrations of critical metals. To the west of the LLSZ, the voluminous Slave granitoid exhibits numerous pegmatitic phases with elevated lithium contents and key geochemical indicators such as low Mg/Li and Nb/Ta ratios that are promising for lithium-cesium-tantalum pegmatite exploration. The uranium potential in the region is confirmed by the presence of numerous historical occurrences, an abundance of radiometric anomalies identified with handheld gamma-ray spectrometers, and widespread elevated equivalent uranium radiometric values observed along shear zones. Notable uranium concentrations were found in leucogranites and pegmatites associated with shear zones in the Spider Lake and Cherry Lake areas.

This work was completed under the Mineral Grant provided by the Government of Alberta on June 22, 2021.